It typically involves many steps, including lithography, deposition, etching and etc., to form a plurality of integrated circuit (IC) chips on a wafer. Due to the complication of the manufacturing process, some chips are inevitably defective. Therefore, the chips are tested for functional defects before the wafer is sent to dicing preparation.
Please refer to FIG. 1A, which shows a conventional probing device 10. The conventional probing device 10 includes a circuit board 12, a space transformer 14, and a probe assembly 16. The space transformer 14 is disposed on the circuit board 12 with an interface composed of a plurality of solder balls 142. The probe assembly 16 is disposed on the space transformer 14 and has a plurality of probes 162, by which the chips on the wafer are tested. Conductive wires (not shown) within the space transformer 14 are used to electrically connect the probes 162 of the probe assembly 16 to the conductive wires on the circuit board 12. In such a configuration manner, testing signals received by the probes 162 can be transmitted to the circuit board 12 via the space transformer 14.
Please refer to FIGS. 1A and 1B simultaneously, in which FIG. 1B shows a force distribution of the space transformer 14 as shown in FIG. 1A. For a better presentation of the distribution of a force F1, the probes 162 are not shown in FIG. 1B. A plurality of pads 141 are distributed over the space transformer 14. When the probing device 10 is running or operating, the probes 162 of the probe assembly 16 contact a device under test (DUT) while a counter force is applied onto the probes 162 by the DUT in such a manner that the probes 162 applies a force F1 to the space transformer 14.
Although the solder balls 142 disposing between the space transformer 14 and the circuit board 12 can support and prevent the space transformer 14 from deformation, some portions of space transformer 14 located on a plurality of gaps 143 between the solder balls 142 receive little structural support and thus plastically deform toward the circuit board 12 resulted from the force F1. The smaller the size of IC chip is, the denser of the distribution of the probes 162 becomes, and thus the bigger the force applies on a unit area of the space transformer 14. The space transformer 14 is, therefore, much more easily deformed by the force F1, and thus flatness of the space transformer 14 as well as that of the probe card is affected. The worse the flatness of the probe card is, the bigger the over drive needs to be. That is, the force has to be large or sufficient enough to enable the probes 162 to practically contact the corresponding pads on the space transformer 14. However, such a bigger amount of force results in more serious deformation of the space transformer 14 and more wear to the probes 162 themselves, thereby shortening the service life of the space transformer 14 and the probes 162.
Moreover, even though the probing devices 10 in the market are manufactured by specialized manufacturers, most of the space transformers 14 are still provided by IC manufacturers or IC designers for cost concerns. There is a trend that those space transformers 14 provided are thereby becoming thinner and thinner. However, a thinner space transformer 14 may deform even more seriously once pressed by the force F1.
Please refer to FIG. 1C for another conventional probing device 10′, in which a protecting gel 144 is filled between the circuit board 12 and the space transformer 14 to prevent the solder balls 142 from being polluted. Although the protecting gel 144 can be used to support the space transformer 14, there might still be gaps found between the space transformer 14 and the protecting gel 144 because of the lower hardness/rigidity and uniformity of the protecting gel 144. If the space transformer 14 cannot effectively contact the protecting gel 144, the supporting ability of the protecting gel 144 cannot be brought into full play, either.
Therefore, it is of concern to those skilled in the art as how to avoid the space transformer 14 from deformation caused by the force F1.